The present invention relates to a method for monitoring the thickness of at least one friction partner of a vehicle friction brake, especially the brake linings of a vehicle braking system; for each braking action, the actuating time, the brake actuating pressure, the relative speed between the brake lining and the moving brake element, as well as the prevailing temperature in this region, being taken into account in a wear model, in such a manner, that the wear determined by the wear model is subtracted from a starting thickness of the friction partners, in particular, of the brake linings.
In regard to the background information, reference is made to both German Published Patent Application No. 34 07 716 and German Patent No. 43 16 993.
In motor vehicles, the brake disks and, in particular, brake linings must be monitored in regular intervals for their state of wear, using checks or visual inspections. In addition, it is known that, in order to sense the state of wear of the brakes, especially the maximum allowable wear of the brake pads of disk brake systems, either an electrically conducting, sliding contact integrated in the brake pad, or alternatively, a wear sensor (so-called xe2x80x9cwear pillxe2x80x9d) separately installed in or on the brake pad, is provided with one or more internal sliding contacts. Depending on the specific embodiment, and in response to a selected, critical degree of wear of the brake pad, i.e. when the wear sensor is exposed, an electrically conducting contact point comes into contact with the brake disk, thereby causing an electrical short circuit or disconnecting an electrical, sliding contact, i.e. an externally imposed flow of electrical current is interrupted. The respective change of the electrical state can then be communicated to the driver, using a suitable evaluation or display unit. For the most part, this display is accomplished by activating a brake warning light in the instrument panel of the motor vehicle, whereby the driver is informed of the necessity of replacing the brake pad.
Because of structural conditions and the high thermal loading of the brake linings and wear sensors, the above-described technique of sensing wear and displaying it generally allows only the display of a few individual, discrete wear stages of a vehicle brake lining. In order to have a longer-term overview of a possibly required change of brake lining, a continuous evaluation and display of the wear state of vehicle brake linings would be desirable.
In principle, this is possible by way of a simulation model, that is, the wear of the brake linings is continuously calculated from their determined loading. This is described in principle in the document German Published Patent Application No. 34 07 716 mentioned at the outset, which includes a device and a method for measuring the thickness of parts subject to wear, and especially, for monitoring the brake linings in a motor vehicle. In order to be able to indicate the wear of these parts subject to wear, i.e. brake linings, the actuating time, the applied brake pressure, and the relative speed of the parts subject to wear (i.e. the relative speed of the brake lining with respect to the brake disk, or in general, with respect to a so-called moving brake element) are measured during each braking action, and are evaluated in an evaluator, using a so-called wear model stored therein, and the corresponding result is displayed.
In this context, the document German Patent No. 43 16 993, which is also mentioned at the outset, constitutes additional related art. It describes a method for determining the state of a vehicle braking system, where, in order to determine the residual thickness of the brake lining, the values of quantities influencing the residual thickness of the brake lining are ascertained during the time of each braking action, and where the frictional work and friction power to be performed and transmitted by each brake lining are calculated using these ascertained values, and are utilized for determining the residual thickness of the brake lining. In this context, the starting thickness values of the brake linings are initially stored, and at least the vehicle weight, the vehicle motion, the rotational motion of the wheels, and the inclination of the road are utilized as the variables influencing the residual thickness of the brake lining, and as the measured variables determining the energy balance of the vehicle. During the respective braking action, the frictional work performed is then calculated, using the measured values for the measured variables determining the energy balance of the vehicle, by considering the energy balance, and, using the calculated frictional work, the ascertained, measured values, as well as a corresponding, stored, so-called wear-thickness frictional-work characteristic, the brake-lining wear-thickness values assigned to the respective braking action are ascertained, according to which the brake lining wear thickness values ascertained for the respective brake application are subtracted from the residual thickness values existing prior to this braking action, and the newly determined, residual thickness values are stored.
With the increasing use of vehicle stability control systems in motor vehicles, the wheels are increasingly decelerated in a selective manner; that is, in the case of a four-wheel passenger car, for example, only the left rear wheel is decelerated, or the right rear wheel is decelerated more sharply than the left front wheel. Of course, this leads to uneven wear on the individual brake linings of the individual vehicle wheels, so that a global simulation or wear model, as described in the known related art, i.e. in the two acknowledged documents, does not supply sufficiently accurate results.
Therefore, an object of the present invention is to provide a correspondingly improved method for monitoring the thickness of the brake linings of a vehicle braking system.